It is known to react pentaerythritol polyols with either a trivalent or pentavalent phosphorus compound in order to form a heterocyclic compound containing phosphorus which is derived from the foregoing class of reagents One compound of this type is pentaerythritol phosphate which can be formed by the reaction of pentaerythritol and phosphorus oxychloride in solvent. U.S. Pat. No. 4,454,064 indicates that a variety of solvents have been used in the past in such a reaction. For example, petroleum ether and benzene are identified as solvents which had been used before the invention described in U.S. Pat. No. 4,454,064. Representative solvents which are described in this patent include dioxane, the preferred solvent, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, chlorobenzene, toluene, xylene, acetonitrile, sulfolane, and tetrachloroethylene. The solvents are indicated as being ones which should have a boiling point of at least 75.degree. C., preferably in the range of 75.degree. C. to about 125.degree. C.